We have recently begun in vivo human studies that are directed at investigating the role of GHRH in GH secretion, using as a tool, a specific antagonist to GHRH, GHRH-Ant. These studies have allowed us to definitively assign an important role to GHRH in the generation of spontaneous GH pulses in humans as well as to determine that the GH responses to L-dopa and arginine are GHRH dependent. We are now extending our preliminary investigations to explore the mechanisms responsible for GH deficiency in the elderly by determining the dose responses of GH to GHRH-Ant.